Certain alpha-olefin copolymers, generally in combination with tackifiers and flow promoters, have been used to produce adhesive compositions that yield a significant bond strength after application, show good paper adhesion (e.g. fiber tear on Kraft paper), minimum peel strength of 500 g/cm, low color and low odor.
Many of the alpha-olefin copolymers currently used in adhesive compositions are derived predominantly from ethylene (see, for example, International Patent Publication Nos. WO98/03603 and WO99/24516). For example, U.S. Pat. No. 6,221,448 discloses a cold seal composition comprising from about 10 wt % to 100 wt % of at least one homogeneous linear or substantially linear ethylene/alpha-olefin copolymer, wherein the alpha-olefin has 3 to 20 carbon atoms, such as octene-1, and the copolymer is produced using a single site metallocene catalyst. The cold seal composition is characterized as having a storage modulus (G′) at 25° C. ranging from about 1×106 dynes/cm2 to about 1×109 dynes/cm2.
Copolymers derived predominantly from propylene have also been proposed for use in adhesive compositions. For example, U.S. Pat. No. 3,954,697 discloses a single component, hot-melt, pressure-sensitive adhesive based on propylene/higher 1-olefin copolymers containing 40-60 mole % of the higher 1-olefin. Suitable comonomers include 1-hexene, 1-heptene, 1-octene, 1-nonene and 1-decene. The copolymer has a melt viscosity range at 190° C. of 10,000 cp. to 75,000 cp, a density of 0.85 to 0.86, a glass transition temperature of −30 to −45° C., and has no melting point measurable by Differential Scanning Calorimetry. Thus the copolymer is amorphous with no residual crystallinity or crystallinity of a very low order. The copolymer is produced using a Ziegler-Natta catalyst.
JP62-119212-A2 discloses a random copolymer with from 40-90 mole % of propylene, from 10-60 mole % of an alpha-olefin such as butene, hexene, and 4-methylpentene produced using an ethylene-bis(tetrahydro-indenyl) zirconium dichloride as a catalyst. However, the Examples in JP62-119212-A2 give products having widely varying characteristics. Example 6 polymerizes propylene and hexene to give 60 percent of units derived from propylene and 40 mol % of units derived from hexene to give a copolymer with 26% crystallinity and a melting point of 123° C. Example 3 uses propylene at 45 mol % to produce a copolymer with a melting point of 50° C. and a crystallinity 7%. The copolymers are said to have anti-blocking characteristics and would be of no use in adhesive applications.
U.S. Pat. No. 6,627,723 discloses a poly-alpha olefin copolymer comprising (a) from 60 to 94 mol % of units derived from one alpha mono-olefin having from 3 to 6 carbon atoms, preferably propylene; (b) from 6 to 40 mol % of units derived from one or more other mono-olefins having from 4 to 10 carbon atoms and at least one carbon atom more than (a), preferably butene-1, hexene-1 or octene-1; and (c) optionally from 0 to 10 mol % of units derived from another copolymerizable unsaturated hydrocarbon, different from (a) and (b), preferably ethylene; wherein the diad distribution of component A in the inter-polymer as determined by 13C NMR divided by the calculated Bernoullian diad distribution is less than 1.07; and wherein the storage modulus G′ of the copolymer determined on cooling, measured at 1 Hz, intersects 3×105 Pa at an intersection temperature of less than 85° C. The copolymer is produced by copolymerizing the monomers in the presence of a single site metallocene catalyst, preferably a bridged chiral bis-indenyl metallocene catalyst. The copolymer is largely amorphous and is said to be useful as a hot melt adhesive, both with and without the addition of tackifying resins.
U.S. Pat. No. 6,747,114 discloses an adhesive composition comprising a semi-crystalline copolymer of propylene and at least one comonomer selected from ethylene and C4 to C20 α-olefins having a propylene content of greater than 65 mole percent; wherein the copolymer has a weight average molecular weight (Mw) from about 15,000 to about 200,000; a melt index (MI) from about 7 dg/min to about 3000 dg/min as measured by ASTM D 1238(B); and a weight average molecular weight/number average molecular weight ratio (Mw/Mn) of approximately 2. In Example 4, propylene is copolymerized with between 11 and 19 wt % 1-hexene at a temperature of 76° C. to 90° C. over a catalyst comprising dimethylsilandiylbis(2-methyl-4-phenyl-1-indenyl)zirconium dimethyl activated with dimethylanilinium-tetrakis(pentafluorophenyl)borate to produce semi-crystalline copolymers having a melting temperature, Tm, between 93° C. and 107° C., a heat of fusion, ΔH, between 58.5 and 96.6 J/g and a melt viscosity at 190° C. of between 2230 and 66,000 cps. Pressure sensitive hot melt adhesives are formed by blending 30 wt % of each copolymer with 50 wt % of Escorez® 5380 tackifier and 20 wt % of Kaydol Oil and the resulting adhesives exhibit a tensile strength in excess of 127 psi, an elongation in excess of 368% and a Shear Adhesion Failure Temperature (SAFT) to Kraft paper of 74° C. to 83° C. In addition, for the copolymer formed from 19 wt % 1-hexene, a hot melt adhesive is formed by blending 80 wt % of the copolymer with 15 wt % of Escorez® 5380 tackifier and 5 wt % of Kaydol Oil. The resulting adhesive exhibits a tensile strength of 1452 psi, an elongation of 768% and a Shear Adhesion Failure Temperature (SAFT) to Kraft paper of 102.5° C. All of the adhesives formed had at least 20% of the other ingredients due to the high molecular weight of the starting copolymers, and had a long set time.
Despite these advances, it has proved difficult to develop a single adhesive composition that exhibits a good combination of properties, such as adhesion at low and high temperatures, set time, thermal stability and mechanical strength, while maintaining low application viscosity. Thus, individual copolymers rarely possess the necessary combination of properties required for adhesive applications. In an attempt to address this problem, two or more polyolefins having different characteristics have often been blended together in the hope of combining the positive attributes of the individual components. However, typically the result is a blend that displays an average of the individual properties of the individual resins.
For example EP 527589 discloses blends of flexible, low molecular weight amorphous polypropylene with higher molecular weight isotactic polypropylene to obtain compositions with balanced mechanical strength and flexibility. These compositions show better flexibility than isotactic polypropylene alone, but are still lacking in other physical attributes. Physical blends also have the problems of inadequate miscibility. Unless the components are selected for their compatibility, they can phase separate or smaller components can migrate to the surface. Reactor blends, also called intimate blends (a composition comprising two or more polymers made in the same reactor or in a series of reactors), have therefore been proposed to avoid the miscibility problems associated with physical blends.
For example, US Patent Application Publication No. 2004/0138392, published Jun. 15, 2004, discloses a continuous process for producing an adhesive comprising 1) selecting a first catalyst component capable of producing a polymer having an Mw of 100,000 or less and a crystallinity of 5% or less under selected polymerization conditions; 2) selecting a second catalyst component capable of producing polymer having an Mw of 100,000 or less and a crystallinity of 20% or more at the selected polymerization conditions; 3) contacting, in a solvent and in a reaction zone under the selected polymerization conditions, the catalyst components in the presence of one or more activators with one or more C3 to C40 olefins, and, optionally one or more diolefins; 4) at a temperature of greater than 100° C.; 5) at a residence time of 120 minutes or less; 6) wherein the ratio of the first catalyst to the second catalyst is from 1:1 to 50:1; 7) wherein the activity of the catalyst components is at least 50 kilograms of polymer per gram of the catalyst compounds; and wherein at least 80% of the olefins are converted to polymer; 8) withdrawing polymer solution from the reaction zone; 9) removing at least 10% solvent from the polymer solution; 10) quenching the reaction; 11) devolatilizing the polymer solution to form molten polymer; 12) combining the molten polymer and one or more additives in a static mixer; 13) removing the polymer combination from the static mixer; and 14) pelletizing or drumming the polymer combination.
In particular, Example 71 of US Patent Application Publication No. 2004/0138392 discloses the production of a copolymer of propylene, hexene and 1,9-decadiene by feeding propylene (14 g/minute or 81 wt %), hexene (3.29 g/minute or 19 wt %) and 1,9-decadiene (0.206 ml/min) to a liquid filled, single-stage continuous reactor using a mixed metallocene solution catalyst system comprising dimethylsilylbis(2-methyl-4-phenylindenyl) zirconium dimethyl and dimethylsilyl-(tetramethylcyclopentadienyl) (cyclododecylamido) titanium dimethyl at a temperature of 115° C. The product, comprising both amorphous and semi-crystalline propylene copolymers, had a Tm of 89.8° C., a Tc of 42.6° C., a glass transition temperature, Tg, of −15.2° C., a heat of fusion of 27.0 J/g and a viscosity of 524 cp at 190° C. and, when used as an adhesive without additives, exhibited a set time of 3.5 seconds and 80% fiber tear at 20-25° C. using file folder as a substrate. When formulated with 2 wt % of Escorez® 5637 tackifier and 5 wt % of Paraflint H1 wax, copolymer of Example 71 provided an adhesive with a set time of 2 seconds and 90% fiber tear at 20-25° C. on a file folder. However, the formulated adhesive would have no fiber tear and poor adhesion at low temperature (−18° C.) on difficult substrates such as Inland paper board.
According to the present invention, there is provided an in-reactor blend of propylene copolymers in which the composition and properties of the individual components are controlled so that the resultant blend, when combined with small quantities of wax and/or a functionalized polyolefin, exhibits an excellent balance of adhesive properties, including a good low temperature (−18° C.) adhesion performance, short set time and a high toughness at relatively low application viscosity.